LONDON -- The FTSE 100 (FTSEINDICES: ^FTSE) has had a bit of a mixed week, dropping 39 points to 6,691 by the end of Thursday, after a few weak Christmas trading updates. But the index of top U.K. stocks recovered on Friday, to finish with a weekly gain of just 9 points.

Sentiment seems mildly positive, although it was tempered by slightly disappointing U.S. jobs figures.

Here are four of the week's biggest FTSE 100 movers.

Marks & Spencer (MKS -0.35%)
Marks & Spencer surprised a few this week, with a 24.8 pence (5.6%) rise to 468.8 pence, even though the quarter to Dec. 28 brought in yet another fall in like-for-like clothing sales, with general merchandise down 2.1%.

But chief executive Marc Bolland blamed "an exceptionally unseasonal October" and highlighted a total general merchandise rise of 1.5% in the eight weeks to Christmas Eve. Overall group sales for the quarter gained 3.2%.

Persimmon (PSN -0.75%)
Housebuilder Persimmon continued its strong run, after an update ahead of full-year results told us of "a strong finish to the year." House sales during 2013 rose by 16% to 11,528, with a 4% increase in the average selling price to 180,900 pounds.

The stock price picked up 95 pence (7.5%) to 1,354 pence, taking it up around 55% over the past 12 months. There are further strong earnings rises forecast for 2014 and 2015.

Wm Morrison Supermarkets (MRW)
A disappointing Christmas trading update from Wm Morrison Supermarkets sent the company's stock crashing 22.1 pence (8.6%) this week, to 236.1 pence. Morrison, which has yet to offer online shopping to its customers, suffered from the omission in a period when rivals were seeing their online sales soar -- like-for-like sales in the six weeks to Jan. 5 fell 5.6%.

In partnership with Ocado, Internet sales should finally start this month, so maybe we'll see a better Christmas next year.

ARM Holdings (ARM)
ARM Holdings, the designer of chips that power Apple's iPhones and a range of other mobile devices, saw its stock climb by more than 25% in the year ending Dec. 31. But with the soaring price giving us a P/E of nearly 55 on full-year expectations, was that valuation a bit too high?

There was a bit of a correction this week after a broker downgrade, with the price dropping back 115 pence (10.6%) to close Friday at 972 pence -- that P/E is now down to a mere 47!

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